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MCB 2050 > Endomembrane System - ER to Golgi > Flashcards

Endomembrane System - ER to Golgi Flashcards

1
Q

2 fates of nascent protein in ER

A

retained ER
exit from ER

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2
Q

2 fates of nascent proteins that remain in ER

A

stay localized in RER
move laterally through ER lumen or membrane bilayer to another ER subdomain

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3
Q

where do the proteins that exit ER initially go

A

ER exit sites (ERES)

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4
Q

what are ERES

A

ER subdomain involved in formation of transport vesicles destined for Golgi

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5
Q

where are ERES usually located

A

next to cis face of Golgi complex

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6
Q

what else is ERES machinery also responsible for

A

proper packing of vesicle with correct lumenal and membrane cargo proteins

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7
Q

why do vesicles at ERES have distinct morphology

A

due to layer of soluble coat proteins (COPS)

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8
Q

what can be found attached to the cytoplasmic surface of nascent vesicle membrane

A

COPs

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9
Q

2 main functions of COPs

A
  1. mediate membrane curvature and formation of vesicle
  2. recognize and concentrate specific cargo components into vesicle
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10
Q

3 major classes of coat proteins

A

COPII
COPI
Clathrin

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11
Q

how do COPII coated vesicles move

A

forward from ERES to Golgi - anterograde transport

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12
Q

how do COPI-coated vesicles move

A

backward from Golgi to ER and backward within Golgi - retrograde transport

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13
Q

how do clathrin -coated vesicles move

A

from Golgi to endosomes or from plasma membrane to endosomes

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14
Q

what is Sar1

A

soluble COPII component - a GTPase

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15
Q

what is Sec12

A

an ER intergral membrane protein

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16
Q

how does Sec12 function

A

as a GEF that catalyzes exchange of GDP for GTP on Sar1

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17
Q

what are Sec23 and Sec24

A

soluble proteins form ternary complex with Sar1 at ERES membrane surface

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18
Q

where are membrane cargo proteins destined for

A

exit to ERES for Golgi

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19
Q

what do membrane cargo receptor proteins do

A

bind to soluble lumenal cargo proteins destined to exit ERES for Golgi

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20
Q

what are membrane trafficking proteins required for

A

subsequent trafficking and docking nascent vesicle with proper acceptor membrane

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21
Q

what is the most common ER export sorting signal

A

di-acidic ER export signal (-Asp-X-Glu)

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22
Q

where is the ER export sorting signal located

A

cytoplasmic-facing-domains of Sec24 selected vesicle membrane proteins

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23
Q

are ER export signals found on ER resident proteins

A

NO

24
Q

Sec13 and Sec 31

A

self assemble to outer cage-like lattice of growing COPII vesicle to act as structural outer scaffolding for growing COPII vesicle bud

25
Q

what does the nascent ERES-derived vesicle contain

A

soluble and membrane protein cargo
molecular machinery

26
Q

where does the vesicle traffic to from ERES

A

cis-golgi networks

26
Q

how does the cis-golgi network (CGN) get formed

A

incoming nascent vesicle fuse with one another to form CGN

27
Q

what does the CGN consist of

A

interconnected network of vesicles and tubules located on cis face of Golgi complex

28
Q

what is the CGN often immediately adjacent to

A

ERES

29
Q

what does movement of vesicles through cytoplasm get mediated by

A

cytoskeleton highways
molecular motors

30
Q

what are Rab proteins

A

large family of lipid-membrane anchored, GTP binding proteins associated with all transport vesicles

31
Q

what are Rab proteins key for

A

regulating vesicle trafficking and fusion

32
Q

what are Rab effector proteins

A

proteins located on a target membrane that include cytoskeleton motor proteins and bind to activated Rab

33
Q

molecular bridge

A

when unique vesicle Rabs associate with Rab effectors on specific target membranes

34
Q

what does the binding of Rab and Rab effector convey

A

vesicle targeting specificity and docking

35
Q

what are SNARE proteins

A

large family of integral membrane bound proteins located on all transport vesicles AND all target membranes

36
Q

what do SNARES do

A

mediate
provide vesicle targeting specificity
fusion of vesicle to target membrane

37
Q

what are the 2 main classes of SNARE proteins

A

v-SNAREs
t-SNARES

38
Q

where are v-SNARES found

A

transport vesicle membranes

39
Q

where are t-SNARES found

A

target (acceptor) membranes

40
Q

where are v-SNARES incorporated into

A

vesicle membrane at site of budding on donor membrane compartment

41
Q

what do all SNARE proteins possess

A

SNARE-motif

42
Q

what is the SNARE motif

A

cytoplasmic-facing, coiled coil domain that extend from vesicle/target membrane surface

43
Q

what are NSF and SNAP

A

cytosolic (soluble) proteins that bind SNARE complexes and unwind SNARE domains linking v/t-SNAREs

44
Q

how do NSF and SNAP unwind SNARE domains

A

ATP hydrolysis

45
Q

what are the fates of soluble and membrane cargo proteins from ER

A

either remain in CGN or move to other compartments in endomembrane system

46
Q

what happens to most ER resident proteins

A

they are retained in ER by exclusions from budding COPII transport vesicles at ERES

47
Q

what happens to escaped ER resident proteins

A

they are returned from CGN back to ER (retrograde transport) by specific ER retrieval sorting signals

48
Q

what do most resident soluble ER proteins possess

A

C-terminal -KDEL sequence

49
Q

what does the C-terminal -KDEL sequence serve as

A

ER retrieval sorting signal

50
Q

what is the KDEL receptor

A

integral transmembrane protein - lumenal-facing domain binds to KDEL sequence of escaped ER proteins

51
Q

what does COPI protein coat recognize

A

cytoplasmic-facing domain of KDEL receptor
-KKxx sequence

52
Q

why can KDEL receptor return to CGN via COPII-coated ERES vesicles

A

KDEL receptor has di-acidic ER export sorting signal that is recognized by Sec24

53
Q

what do most resident ER membrane proteins possess

A

cytoplasmic facing, C-terminal dilysine (-KKxx) sequence

54
Q

why does -KKxx sequence serve as

A

ER retrieval sorting signal

MCB 2050 (11 decks)

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